How to Read from stdin in Haskell
In haskell there are two ways to read the stdin stream. Which one to use depends on what you’re trying to accomplish I guess.
Either you can read each line in a loop.
import System.IO main = myLoop myLoop = do done <- isEOF if done then putStrLn "" else do inp <- getLine putStrLn inp myLoop
We call the myLoop function recursively until getLine returns EOF. Every time we get a string back, we print it to stdout and call ourselves again.
The other method involves reading the entire stream with getContents and then lazily read each line.
import Data.Char main :: IO () main = do inp <- getContents let ls = lines inp mapM_ putStrLn ls
Here we get the stream into inp, split that into an array of lines, and map that array to the putStrLn function, which prints to stdout.